Add IDL and initial Blink API for Background Sync

Source/modules/background_sync/SyncManager.idl

Index: Source/modules/background_sync/SyncManager.idl
diff --git a/Source/bindings/tests/idls/core/TestPartialInterface4.idl b/Source/modules/background_sync/SyncManager.idl
similarity index 31%
copy from Source/bindings/tests/idls/core/TestPartialInterface4.idl
copy to Source/modules/background_sync/SyncManager.idl
index 524087cdbe82c7bb84404ffd80b87cabb483e262..9dff2924e46fb1cdb0f4d1610302de07870eceab 100644
--- a/Source/bindings/tests/idls/core/TestPartialInterface4.idl
+++ b/Source/modules/background_sync/SyncManager.idl
@@ -3,8 +3,13 @@
 // found in the LICENSE file.
 
 [
-    Conditional=FOO,
+    //FIXME: Expose on ServiceWorker as well

[Michael van Ouwerkerk, 2015/03/02 14:19:11]

Why is this not exposed on ServiceWorker yet?

[iclelland, 2015/03/05 04:32:49]

I just wasn't sure if there were complications around making some of the methods
window-only, so for early development I left it off of the service worker global
scope.. That is no longer a requirement, so I've fixed this.

Done.

+    Exposed=(Window),
+    GarbageCollected,
+    RuntimeEnabled=BackgroundSync,
     TypeChecking=Interface,
-] partial interface TestInterface3 {
-    [Conditional=BAR, TypeChecking=Unrestricted] static void voidMethodDocument(Document document, double d);
+] interface SyncManager {
+    [CallWith=ScriptState,ImplementedAs=registerFunction] Promise<SyncRegistration> register(optional SyncRegistrationOptions options);
+    [CallWith=ScriptState] Promise<sequence<SyncRegistration>> getRegistrations();
+    readonly attribute unsigned long minAllowablePeriod;
 };